Physics Nobel Prize
awarded to
Stanford's Steven Chu
At first blush the idea of cooling groups of atoms,
dramatically slowing their normally frantic motion by
illuminating them with laser light, seems impossible.
Normally, shining light on something heats it up.
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In 1985, however, Steven Chu and his
colleagues at AT&T Bell Laboratories found special
circumstances where lasers formed what Chu dubbed
"optical molasses," a condition where the
intense light acted to slow the motion of target atoms
much like the motion of a marble is slowed when it
plunges into actual molasses. They also developed the
first atomic trap that held the chilled atoms in place,
instead of letting them fall under the influence of
gravity.
That research has now earned Chu, the
Theodore and Frances Geballe Professor of physics and
applied physics, a share of the 1997 Nobel Prize in
physics. Co-recipients of the award are Claude
Cohen-Tannoudji, a professor at the Collège de France
and École Normale Supérieure in Paris, and William D.
Phillips, who works at the National Institute of
Standards and Technology in Gaithersburg, Maryland.
By slowing atoms down from typical
speeds of 4,000 kilometers per hour to speeds of less
than a tenth of a kilometer per hour, optical molasses
had made these atoms much easier to study. Instead of
rapidly disappearing, atoms caught in optical molasses
form what to the naked eye looks like a glowing cloud the
size of a pea. Previously, scientists could control the
speed of electrically charged atoms by using electrical
and magnetic fields. Optical molasses extended this
capability to electrically neutral atoms for the first
time.
As the Nobel prize committee mentioned,
this technique has proven to be a powerful tool for
increasing scientific knowledge about the interplay of
light and matter. In particular, it has provided
scientists with a greater understanding of the
quantum-dynamical nature of gases at extremely low
temperatures. Building on this work, for example, other
scientists have been able to create a bizarre new state
of matter, whose existence was originally postulated by
Albert Einstein 70 years ago. In this state of matter,
called a Bose-Einstein condensate, a group of atoms is
chilled to such a low temperature that the atoms' motion
nearly stops and they begin acting like a single entity,
a kind of super atom.
Scientists are using these techniques
to design more precise atomic clocks for use in space
navigation, atomic interferometers to provide
ultra-precise measurements of gravitational forces, and
atomic lasers, which might one day be used to manufacture
extremely small electronic components.
Much of Chu's work at Stanford has been
to apply and extend these techniques in new areas. Among
other things, Chu and his students have constructed an
atomic fountain. Laser-cooled atoms are sprayed upward
from an atomic trap like a jet of water. At the very top
of the trajectory, the atoms are almost motionless for an
instant. At that moment microwaves are beamed at them
that provide information about the atoms' inner
structure. This may provide the basis for an atomic clock
with a precision one hundredfold greater than at present.
Chu's laboratory also has been applying
an interesting spin-off of the technique to study the
physical characteristics of individual polymer molecules:
a marvelous tool called optical tweezers. It is a kind of
microscopic version of a Star Trek tractor beam. The
scientists can use laser light to grip and manipulate a
number of different kinds of microscopic objects immersed
in water.
In two papers published earlier this
year, the scientist and his students have demonstrated
that studying polymers one-by-one can provide important
new insights into the way in which the properties of
polymeric materials, like plastics and synthetic and
biological fibers, arise from the collective action of
large numbers of individual molecules. In one study, the
researchers found that individual polymer molecules
appear to express a surprising degree of individuality.
When forced to unravel in a strong current, apparently
identical molecules unwind in highly individual and
unpredictable ways.
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